Automobile manufacturers continuously strive to improve fuel efficiency. Efforts to improve fuel efficiency, however, are typically offset by the need to provide enhanced comfort and convenience to the vehicle operator. For example, it is well known that manual transmissions are more fuel efficient than automatic transmissions, yet a majority of all passenger vehicles are equipped with automatic transmissions due to the increased convenience they provide.
More recently, “automated” variants of conventional manual transmissions have been developed which shift automatically without any input from the vehicle operator. Such automated transmissions typically include a plurality of power-operated actuators that are controlled by a transmission controller to shift traditional synchronized dog clutches. However, such automated transmissions have the disadvantage that there is a power interruption in the drive connection between the input shaft and the output shaft during sequential gear shifting. Power interrupted shifting may result in a harsh shift feel which is generally considered to be unacceptable when compared to the smooth shift feel associated with most automatic transmissions. To overcome this problem, automated twin-clutch transmissions have been developed which can be powershifted to permit gearshifts to be made under load. Examples of such automated manual transmissions are shown in U.S. Pat. Nos. 5,966,989 and 5,890,392. While such powershift twin-clutch transmissions overcome several drawbacks associated with conventional single-clutch automated transmissions, a need exists to develop simpler and more robust transmissions which advance the automotive transmission technology.
In particular, it may be advantageous to position the clutches at opposite ends of the transmission to provide maximized cooling. Additionally, by positioning the clutches in this manner, each clutch assembly may be appropriately sized without the requirement that the shift clutch be packaged within the start clutch. Furthermore, depending on the location of the output shaft of the transmission, it may be possible to provide drive torque to front and rear propeller shafts without the use of a separate transfer case.